[jmf]

I really hear the e12 relays tripping. What could come and be an issue from the analog input of the SOHA II amp ?
 
JMF

 

[Nevohteeb]

If I remember correctly the e12 is also a DC current protection circuit. Maybe your source is not well connected to earth ?

You should try another source ?

 

[jmf]

I have to consider this hint. Thanks,
 
JMF

 

[Navyblue]

So no fix proposal for this e12 trip issue?

Best regards,

JMF

Btw, did you implement the regal mod? Or the higher heater current mod?

Mine used to trip often if I set the B+ or the current too high. Then it happens when I used 12BH7 that draw more heater current (300mA) than stock (150mA). I suspected it had to do with power instability. But now it seems to trip no matter what I do, although it's been a while since I touched that amp.

 

[jmf]

It is a plain vanilla one, without mods. I use 12AU7. I don't know it it matters.
 
This behavious seems to have been experienced by several users, but not really explained...
 
Regards,
 
JM

 

[muskyhuntr]

Hi,
 
It is possible to reduce the sensitivity of the E12.  This is from AMB's website;

1. If the relay oscillates on and off, and adjusting the VR1 trimpot will not make it stop, then you may reduce the sensitivity of the circuit to tame this behavior by increasing the value of resistors R5-R8 to 22KΩ to 47KΩ.
2. If you encounter false cut-outs when playing program material with loud low frequency content, you may reduce the sensitivity of the circuit as above. Additionally, You can increase the value of C5 to 3.3µF to lower the input filter frequency.
3.  

Hope this helps.
Jim

 

[vixr]

it may be working properly...did you check for DC on the output? The reason I say this is because I built a single 12AU7 tube amp and I run it on a 7Ah sealed lead acid 12v battery...like the kind on a scooter. When the battery starts to run down the DC measured at the output jumps around...like 13-3-8-16-23-1 mA very quickly...maybe the e12 is just doing its job.

 

[jmf]

I come back to you, to have advice about how to check if I have ponctually some DC at the output:
- where would be the best measuring point?
- is it voltage or current to be measured?
 
Regards,
 
JMF

 

[vixr]

jmf,
   Measure DC voltage from output ground to the amplfiers left and right outputs, most easily done at the headphone jack. I usually check this with no source plugged in. You will be looking at the mV scale. Wait at least a minute for the tube to warm up before measuring...

 

[jmf]

Thanks,
 
I'll try as soon as possible,
 
JMF

 

[Navyblue]

You can not measure DC on the output jack with the relay inline, you have to tap it before it hits the E12.

However, if the DC transient is too fast you might not be able to measure it with a DMM, you need a scope for that. But if it stayed on for say a couple of seconds, this you can pick it up on a DMM.

Source or no source it doesn't matter, DC on source won't make it through the coupling cap. So of course if you indeed get DC the culprit is the output stage (the SE buffer circuit.)

 

[vixr]

Navyblue,
    my bad...the only amp I've ever built with the E12 was the old Millett hybrid about 8 years ago...I timed how long it took for the tubes to settle down and set the E12 accordingly. It worked perfectly, so I never had to troubleshoot it. All of my DC offset problems have been with SS amps with no E12.

 

[cfcubed]

Searching this thread for "tripping" yields this: http://www.head-fi.org/t/374941/soha-ii-builders-thread/570#post_5392652
Read down a bit & it talks about how to make pre-e12 offset measurements.   And other related things.

 

[jmf]

Hello,
 
I finally checked this DC issue.
 
I measured the Voltage between ground and R8 (http://www.cavalliaudio.com/diy/soha%20ii/main.php?page=schematics/ampschematic). I use a DMM, as I don't have a scope.
 
It is usually within few mV. But when the e12 trips, I can catch figures above 100 mV (sometimes 200 mV). Thius is for short time... but it is really annoying when listening to music seriously.
 
So it seems that there is an issue in the amp stage. As I have only very basic knowledge in electronics, I have no idea what to look for in this amp stage.
 
I'm going to check if it is the same on the other chanel.
 
Regards,
 
JM

 

[jmf]

So the DC event seems to appear on both channels.
 
What could be the faulty commom cause of those DC events?
 
Regqrds,
 
JMF